Long-term treatment of rats with haloperidol produced an increased sensitivity to apomorphine in various brain regions as assessed by the (14C) deoxyglucose method. Using this method only the zona compacta, lateral habenula and anterior cingulate cortex showed supersensitivity. Supersensitivity in all three regions was antagonized by concurrent treatment with lithium. Chronic treatment of rats with cocaine was found to induce both alpha- and Beta-adrenergic receptor supersensitivity. Concurrent treatment with lithium again antagonized this effect. Chronic lithium was also found to enhance cholinergic supersensitivity induced by chronic scopolamine. Lithium by itself appeared to enhance activity in the cholinergic system.